All cultured cells with rare exceptions require a growth medium of low molecular weight nutrients (DME or Ham's F12) to be supplemented with serum. The serum provides high molecular weight factors required for cellular attachment, survival, and proliferation. Although these factors differ for each line it is possible to identify these individual requirements. Cells which have become transformed or tumorigenic have altered responses to normal growth regulatory pathways. In the work outlined in this grant we will characterize the nutritional requirements for proliferation of a cloned normal rat embryo fibroblast line. We will transform this line with SV40, a small DNA virus, and characterize the way in which the virus/cell interaction has altered the nutritional requiremnts of the line. We will determine the tumorigenicity of the transformants, attempt to correlate the alterations in nutritional requirements with the degree of tumorigenicity, and recharacterize the nutritional requirements of tumor-derived sublines. Transformed cells differ broadly in their properties from normal cells in culture. However, investigators have found recently that many of these growth patterns result from altered responses to serum hormones. In defined media several tumor lines studied reverted to "normal" behavior. We will undertake to identify good correlates of tumorigenicity in defined media for our transformants.